Simon Whitnall 12 November at 12.49
Cheers for the message. As usual it all comes back to the principles. If you remember the gravity and the ground reaction force reaction ones... Well it's gravity pushing down on us and then the foot contact with the ground that causes the knee to bend (flex). Depending on specifically which hamstring muscle we're talking about, it is the muscles job to decelerate and control the bending on the knee (how much, how far, how fast) and the bending of the hip, but also the frontal plane and transverse plane motions at the knee and hip.
I hope that helps mate, it is the short answer, if you want the long answer and you have a couple of days let me know ;-)